All humans seem to divide the world into things they will eat, and things they will not eat. Underlying this division is a conception of the nature of food. Our first approach to this problem will be to refine our previous taxonomy of food dislikes or rejections by adults in American culture. Then, we will study the development of these rejections. Our preliminary work suggests four general categories of food rejection by adults: 1) distasteful substances - rejection because of a disliked taste (e.g. anchovies, black unsweetened coffee); 2) dangerous substances - rejection because of suspected bodily or personal harm (e.g. suspect mushrooms, or a legally or religiously prohibited food); 3) disgusting substances - emotionally loaded rejection of a substance because of the idea of what it is, or its origin (e.g., insects, body excretory products); and 4) inappropriate substances -similar to disgusts, but not heavily emotionally loaded (e.g. grass, sand). The infant seems to reject foods primarily on the ground of distaste; surely it does not have the cognitive ability to reject substances on ideational gounds (disgusting and inappropriate types of rejections). We propose to study the development of disgusting and inappropriate food categories, in children in general "Piagetian" lines, with adults and children of various ages. Food choices and preferences, and measurement of facial and verbal responses to a variety of food and non-food odors and tastes will be determined for this same population. The child's growing understanding of the fate of food in the body and the concept of contamination will be described and analyzed. This will lead to a description of the child's concept of food. This work bears directly on the common and troublesome food rejection syndrome seen in many young children, and on the world problem or rejection of some specific, inexpensive and nutritive foods, in almost all cultures. It is the first study of its type.